The atomic picture of cellulose dissolution in alkali/urea aqueous solution is still not clear.

To reveal it, we use trehalose as the model molecule and total scattering as the main tool. Three kinds

of alkali solution, i.e., LiOH, NaOH and KOH are compared. The most probable all-atom structures

of the solution are thus obtained. The hydration shell of trehalose has a layered structure. The smaller

alkali ions can penetrate into the glucose rings around oxygen atoms to form the first hydration

layer. The larger urea molecules interact with hydroxide groups to form complexations. Then, the

electronegative complexation can form the second hydration layer around alkali ions via electrostatic

interaction. Therefore, the solubility of alkali aqueous solution for cellulose decreases with the alkali

cation radius, i.e., LiOH > NaOH > KOH. Our findings are helpful for designing better green solvents

for cellulose.